Temperature variation makes an ectotherm more sensitive to global warming unless thermal evolution occurs.

Area of Science:

• Ecology and evolutionary biology
• Climate change biology
• Physiological ecology

Background:

• Global warming is altering mean temperatures and daily temperature fluctuations (DTFs).
• Latitudinal differences in intraspecific thermal adaptation are crucial for predicting species' long-term responses.
• The interactive effects of DTFs and mean temperatures on ectotherm populations across latitudes remain understudied.

Purpose of the Study:

• To investigate how DTFs affect ectotherm growth rates at different latitudes under varying mean temperatures.
• To assess the role of local thermal adaptation in mitigating the negative impacts of DTFs.
• To evaluate the combined effects of gradual thermal evolution and increasing DTFs on population growth predictions.

Main Methods:

• A common-garden experiment was conducted using low- and high-latitude populations of the damselfly Ischnura elegans.
• Larvae were exposed to different mean temperatures (20°C and 24°C) and DTFs (0°C, 5°C, and 10°C).
• Growth rates, body condition, antioxidant defence, metabolic rate, and oxidative damage were measured.

Main Results:

• DTFs generally reduced growth and induced stress, particularly at a mean temperature of 24°C.
• Warming benefited growth at low DTF but became detrimental at high DTF, with latitude-specific responses.
• Space-for-time substitution indicated that evolved high-latitude populations may tolerate DTFs better, contrasting with current populations.

Conclusions:

• DTFs pose a significant challenge to ectotherm populations under warming scenarios, with effects modulated by mean temperature and latitude.
• Local thermal adaptation can alter population responses to DTFs, suggesting that evolutionary processes are critical.
• Integrating DTFs and gradual thermal evolution provides a more realistic, yet complex, outlook on global warming impacts.